The folded cardboard trays or clamshell cartons commonly used in "fast food" packaging have basically consisted of a compartment or compartments defined by a flat bottom with peripheral walls either perpendicular to the bottom or angled slightly outward relative to the vertical. The formed tray is adapted for use either as an open container or to receive some form of closure. The clamshell carton basically comprises two generally equal size walled chambers hingedly connected for pivotal closing of one upon the other.
Apparatus for high speed automated formation of such containers is known. In one form of apparatus, flat diecut blanks of paperboard or cardboard are held in a magazine feeder for a gravity feeding of the blanks toward a discharge end of the feeder. One or more vacuum plates, pivotally mounted on a swing arm, pull the blank from the magazine feeder, rotate the blank to a horizontal position, and lower the blank on the top of a compression or forming chamber.
After positioning the blank on the top of the compression chamber and retraction of the vacuum plate, glue tips rotate downward to apply glue at defined points, four in a single compartment tray and eight in a dual compartment clamshell carton. Upon a retraction of the glue tips, a forming head lowers to push the blank through the top of the compression or forming chamber, inwardly folding the blank to overlap the glue points and define the tray or carton. As the formed container moves into the forming chamber it nests into the container folded immediately prior thereto. The sides of the forming chamber are defined by vertical smooth cylindrical rods which retain the formed containers as the containers, whether trays or cartons, are progressively moved downward as each succeeding container is formed. The formed containers are ultimately discharged from the bottom of the forming chamber with the duration of the time within the forming chamber being sufficient to allow the glue to set.